1. Field of the Invention
The present invention relates to an insulated gate semiconductor device having trench.cndot.gate and a manufacturing method thereof.
2. Description of the Background Art
The insulated gate semiconductor device is a semiconductor device having the structure in which p-type and n-type semiconductor layers are alternately joined, main electrodes through which main current flows are electrically connected to the semiconductor layers on both ends, and a gate electrode for forming a channel by applying the electric field is connected to at least one of the semiconductor layers with an insulating film interposed therebetween. In this insulated gate semiconductor device, the current flowing between the two main electrodes, i.e., the main current, is controlled by the voltage applied to the gate electrode. Typical examples thereof include the MOS transistors and the insulated gate bipolar transistors (simply referred to as IGBT).
The IGBTs for electric power generally have the structure in which a large number of IGBT elements (referred to as unit cells, hereinafter) are connected in parallel. It is the same in the MOS transistors for electric power, too. Especially, the insulated gate semiconductor devices having trench.cndot.gate, that is, the devices having the structure in which the gate electrode is buried in the trench formed in the upper surface of the semiconductor substrate have attracted special interest as excellent devices having such advantages as being capable of enhancing the integration degree because of easy miniaturization and simple producing processes. Two examples of the conventional insulated gate semiconductor devices having the Trench.cndot.gate will now be described below.